This invention relates to a process for the preparation of polyurethane foams having improved flame properties based on dispersions containing polymer-containing relatively high molecular weight hydroxyl compounds, in which the flameproofing agent is an expandable graphite used alone or in combination with an inorganic co-flameproofing agent.
Many attempts have been made to make polyurethane foams based on polyether polyols and polyester polyols flame-resistant. Various phosphoric acid esters, as well as metal oxides, have been used for this purpose. British Pat. No. 2,168,706 proposes expandable graphite as a flameproofing agent for polyurethane polyether foams. However, the use of expandable graphite has the disadvantage of a strong wick effect attributable to the graphite component, which leads to continued burning; serious fly-ash formation and, in some cases, incandescent soot formation; and finely powdered cinders that turn very easily into dust.
It has now surprisingly been found that these disadvantages, which are an obstacle to commercial use, do not occur when expandable graphite is used as a flameproofing agent in polyurethane foams based on dispersions of polymer-containing, relatively high molecular weight hydroxyl compounds.
Foams according to the invention exhibit advantageous results upon exposure to flame when compared to polyurethane ether foams as described in British Pat. No. 2,168,706. Even when used alone, but especially when used in combination with inorganic flame-resistant additives, expandable graphite used according to the invention produces foams exhibiting no wick effect produced by the graphite, no fly-ash formation, and no finely powdered cinders, but instead produces foams that are highly carbonizing, self-extinguishing, and non-dripping. The advantages of the invention can be demonstrated by a number of widely applied flameproofing standards, including, for example, BS 5852, Part 2 Crib 5 Test; DIN 4102 MVSS; and UL 94.